Synthesis, Biological and In Silico Studies of Griseofulvin and Usnic Acid Sulfonamide Derivatives as Fungal, Bacterial and Human Carbonic Anhydrase Inhibitors

Abstract

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the essential reaction of CO₂ hydration in all living organisms, being actively involved in the regulation of a plethora of patho-/physiological conditions. A series of griseofulvin and usnic acid sulfonamides were synthesized and tested as possible CA inhibitors. Since β- and γ- classes are expressed in microorganisms in addition to the α- class, showing substantial structural differences to the human isoforms they are also interesting as new antiinfective targets with a different mechanism of action for fighting the emerging problem of extensive drug resistance afflicting most countries worldwide. Griseofulvin and usnic acid sulfonamides were synthesized using methods of organic chemistry. Their inhibitory activity, assessed against the cytosolic human isoforms hCA I and hCA II, the transmembrane hCA IX as well as β- and γ-CAs from different bacterial and fungal strains, was evaluated by a stopped-flow CO₂ hydrase assay. Several of the investigated derivatives showed interesting inhibition activity towards the cytosolic associate isoforms hCA I and hCA II, as well as the three γ-CAs and Malassezia globosa (MgCA) enzyme. Six compounds (1b-1d, 1h, 1i and 1j) were more potent than AAZ against hCA I while five (1d, 1h, 1i, 1j and 4a) showed better activity than AAZ against the hCA II isoform. Moreover, all compounds appeared to be very potent against MgCA with a Ki lower than that of the reference drug. Furthermore, computational procedures were used to investigate the binding mode of this class of compounds within the active site of human CAs.

Keywords: carbonic anhydrase inhibitors; griseofulvin derivatives; in silico studies; stopped-flow CO2 hydrase assay; usnic acid derivatives.

Figure 1

The structure of approved sulfonamide drugs.

Scheme 1

Synthesis of compounds 1a–d.

Scheme 2

Synthesis of compounds 1e,f.

Scheme 3

Synthesis of compounds 1g–j.

Scheme 4

Synthesis of compounds 4a,b.

Figure 2

(A) 2D interaction diagram of compound 4a docking pose interactions with the key amino acids in hCA II, (B) 2D interaction diagram of compound 4b docking pose interactions with the key amino acids in hCA II. (C) Superposition of compound 4a (blue) bound to hCA II in comparison to compound 4b (red) to hCA II, with specific residues labeled. Active site zinc is shown as a blue sphere, red dotted arrows indicate H-bonds, and yellow spheres hydrophobic interactions.

Figure 3

(A) 2D interaction diagram of compound 1i docking pose interactions with the key amino acids in hCA I, hCA II, and hCA IX (B) Superposition of compound 1i (yellow)bound to hCA I in comparison with its binding to hCA II (magenta) and hCA IX (blue) isoforms. Active site zinc shown as blue sphere, red dotted arrows indicate H-bonds, pink arrow halogen bond and yellow spheres hydrophobic interactions.

Figure 4

Drug-likeness model and bioavailability Radar of the compounds 1d and 1i. The pink area represents the optimal range for each property for oral bioavailability, (Lipophilicity (LIPO): XLOGP3 between −0.7 and +5.0, Molecular weight (SIZE): MW between 150 and 500 g/mol, Polarity (POLAR) TPSA between 20 and 130 Ų, Solubility (INSOLU): log S not higher than 6, Saturation (INSATU): fraction of carbons in the sp3 hybridization not less than 0.25, and Flexibility (FLEX): no more than 9 rotatable bonds.